If youâ€™re writing code that looks like User.all.reject(), youâ€™re doing it wrong. Donâ€™t worry though, weâ€™ve all done it before. ActiveRecord makes it all too easy to introduce code that is far from performant, and after awhile, we tend to forget that underneath the pretty API, weâ€™re still producing SQL. In this talk, weâ€™ll peel back the API so that we can see some of the common mistakes I see when dealing with ActiveRecord statements, and more importantly, how you can fix them.